Isospin Dependence of Partial Wave Widths for Antiproton-Nucleon Annihilation from p Stop in Absorption by Light Nuclei

Abstract

Recently, Schneider et al. l ) have reported X-rays from antiprotonic 3He and 4He. They found that the strong absorption occurs mainly from 2p atomic orbit of p. The strong interaction 2p level shifts and the 2p and 3d absorption widths have been measured and summarized together with the existing studies. The optical potential fits are compared with the experimental data. There the 3He absorption widths seem to be reproduced nicely, however, the 2p 4He one appears somewhat below the observed one even with the improved fit which is named a microscopic optical model. The purpose of this paper is to derive the isospin dependence of the partial wave widths for pN stop in absorption from the observed data and predict 15 2H and 15 3H ones. For this purpose we assume a G-parity2) conservation for the pN annihilation into multi pi on states, in addition to the isospin, spin and parity and a single nucleon absorption dominance by the nucleons in the light nuclei of interest. The average over spins and the phase volume are assumed to give no significant difference among the light nuclei under study. We know that the G-parity is not as good quantum number as the isospin. This may be found, e.g., from the comparison of the experimental data 3 ) on J/<P hadronic decays into stable ones and our theoretical study.4) The latter has been done many years ago and based on the data available at that time, however, roughly 10% violation pointed out still holds by better statistics. This quantity may also depend on the energy, so it should be tested directly from experiments. The pion carries an odd G-parity which is a multiplicative quantum number. The conservation of G does not admit the interference between the isospin one and null amplitudes in the pN annihilation, provided that the contribution from kaon pair associated processes is negligible. The binding energies per nucleon for the nuclei with mass number A=2 to 4 are largely different, so that the kinetic energies of them are varying correspondingly. It is necessary to take into account the internal motion of them to the absorption study even if we consider the 15 stop in absorption by nuclei. We shall study the problem by neglecting this effect at first and then examine how much it affects the result thus